Unlike most tissues, cartilage does not self-repair following injury. Cartilage is an avascular tissue made up largely of cartilage specific cells, the chondrocytes, special types of collagen, and proteoglycans. The inability of cartilage to self-repair after injury, disease, or surgery is a major limiting factor in rehabilitation of degrading joint surfaces and injury to meniscal cartilage. Osteoarthritis, the major degenerative disease of weight bearing joint surfaces, is caused by eroding or damaged cartilage surfaces and is present in approximately 25% of the over 50-year-old population. In the US more than 20 million people suffer from osteoarthritis, with annual healthcare costs of more than $8.6 billion. In addition, the cost for cartilage repair from acute joint injury (meniscal lesions, patellar surface damage and chondromalacia) exceeds $1 billion annually. Therefore, new therapeutic approaches are needed to heal lesions of cartilage caused by degeneration or acute trauma.